When riding a wet manned submersible vehicle, a human occupant may be exposed to long duration submersions in water that is at temperatures that may be below normal human comfort, and perhaps even survival, levels potentially leading to hypothermia. This can create significant energy drain and fatigue on the human occupant caused by core thermal cooling processes that result from the human body's response to maintain thermal equilibrium while exposed to such temperatures and rapid exothermic heat loss due to water thermal film coefficients. The result after such exposure can be a drastic reduction in human physical and intellectual performance. In the case of military personnel, at the end of a transit excursion on a wet submersible, this reduction in physical and intellectual performance may occur at the exact time when maximum exertion and optimal decision-making is required.
Currently, underwater thermal protection is provided by wet suits, dry suits, circulatory hot water hydronic heating, and electric heating. The most energy efficient solution is a dry suit that can be worn by the human occupant of the wet submersible vehicle. However a dry suit does not provide the volume or space for an individual of average dexterity to withdraw their hands and arms from the sleeve and glove area of the suit into a main core zone of the dry suit in such a way as to provide tactile access of the wearer to certain dry zones (for example, head, neck, shoulders, torso) with his/her own hands. Further, a dry suit requires open circuit buoyancy, i.e. inflation/pressurization, control by the individual wearing the dry suit. However, variations in the dry suit buoyancy affect the individual's buoyancy and therefore affect the overall buoyancy of the wet submersible vehicle. In addition, air is expelled from the dry suit's dump valve as the buoyancy is adjusted during venting procedures such as during an ascent of the wet submersible vehicle. As expelled air ascends to the water surface it expands due to the decreasing pressure differential, creating a tell-tale eruption of bubbles at the water surface which, in the case of military operations, can undesirably signal the presence of military personnel below.